1. Field of the Invention
The present invention relates to an apparatus for detecting a flaw using supersonic waves to perform non-destructive tests of civil engineering and building structures such as asphalt paved roads, concrete paved roads and external walls of tunnels using a low frequency ultrasonic wave, and more particularly, to an apparatus for detecting a flaw using supersonic waves to accurately measure defect positions and thicknesses without interference by a surface wave.
2. Description of the Related Art
Heretofore, apparatuses for detecting flaws using supersonic waves, used for non-destructive tests of civil engineering and building structures and the like, infer internal states of whether defects such as cavities and the like exist by observing ultrasonic reception waveforms with an oscilloscope through disposing ultrasonic probes for transmission and for reception in a predetermined distance with making water, glycerin, or the like lie between them and a test object. However, since a spot non-destructive test cannot detect internal defects sufficiently and works for changing a measuring point are complicated, the inventor et al., of the present invention have proposed an apparatus for detecting flaws using supersonic waves, i.e., the type of the system shown in FIG. 1 (Japanese Patent Laid-Open No. Hei 5-080,035 published on March 30 in 1994) that performs a non-destructive test of internal states of a civil engineering and building structure using a tire probe having built-in ultrasonic probes for transmission and for reception.
In FIG. 1, a tire probe 302 is provided in free rotation inside a main frame of an apparatus 300. The tire probe 302 is equipped with a rubber tire 304 made of hard urethane rubber, and a Gel sheet 306 outside the tire. As the Gel sheet 306, high polymer Gel of elastic can be used as disclosed in, for example, Japanese Patent Laid-Open No. Hei 1-304,102. Both wheels of the rubber tires 304 are provided with a pivot 308 per each, which is mounted on a probe mounting axle 312 fixed through bearings 310 in free rotation in the main frame of the apparatus 300. In addition, an oil seal 314 is provided inside the bearings 310 so as to prevent outside leakage of medium liquid such as water and the like, filled in the rubber tire 304. A mounting frame 316 is attached to the center of the probe mounting axle 312, a ultrasonic probe for transmission 318 and a ultrasonic probe for reception 320 are mounted on the bottom of the mounting frame 316. From the ultrasonic probe for transmission 318 and the ultrasonic probe for reception 320, signal lines 322 and 324 are wired and connected to a transmission circuit and a receiving circuit respectively, both of which are not shown. Further, auxiliary wheels 326 are provided in the main frame of the apparatus 300 so that stable running of the main frame of the apparatus 300 can be attained.
According to an apparatus for detecting flaws using supersonic waves using such a tire probe, by making the tire probe 302 run on a test object, cross-sectional layer images showing a running distance in a horizontal axis are displayed on a CRT monitor so that an internal defect such as an cavity can be certainly found. However, in an apparatus for detecting flaws using supersonic waves using a tire probe, a surface waves propagated on near a surface of the test object interferes with reflective waves from acoustic discontinuous points inside the test object or from the bottom of the test object. Consequently, this lead to the problems that rise time and existing time of the reflection waves in a reception waveform become unclear, this gives great errors to precision of a non-destructive test, for example, identification of defect position inside the test object and thickness measurement, and this causes impossible measurement.
For example, as shown in FIG. 2, the case that a non-destructive test is performed through rotationally moving the tire probe 302 on a test surface 320 of the test object 328 will be described. Ultrasonic waves transmitted from the ultrasonic probe 318 for transmission built in the tire probe 302 pass a path of water of medium liquid (1), and a propagation path of longitudinal waves in an asphalt paved road (4) and (5), they arrive at the ultrasonic probe for reception 320 through a path in a tire (3), and the ultrasonic probe for reception obtains longitudinal wave reflection echoes including information of thickness H of the test object 328. At the same time, the ultrasonic waves transferred from the ultrasonic probe 318 embedded the tire probe 302 arrives at the ultrasonic probe for reception 320 through the path in the water inside the tire (1), propagation path of the surface waves on the test object 328 (2) and path in the water inside the tire (3). In this case, these waves do not include thickness information of the asphalt paved road, and interfere with the longitudinal wave reflection echo as surface waves becoming disturbing waves upon thickness measurement and the like. Consequently, a reception waveform becomes as shown in FIG. 3, the rise position of the bottom echo becomes unclear, and hence, these waves become obstacles to thickness measurement of the test object.
Besides the tire probe, these conventional problems also arise at apparatuses for detecting flaw using supersonic wave adopting the type of a ultrasonic probe that directly contacts to a test object with an acoustic Contact medium.